1. Field of the Invention
The present invention relates to duplexers for use in a mobile communication transceiver such as an automobile phone or a portable phone.
2. Description of the Related Art
FIG. 5 is a block diagram showing the general components of a duplexer. A duplexer 1 is a composite high-frequency component which protects the transceiver's receiver from transmission power when transmitting and which supplies a received signal to the receiver when receiving, so that the transceiver can use one antenna ANT for both transmitting and receiving. By mounting compact, surface-mount components such as filters F1 and F2 and a switch SW on a highly dense printed circuit board, the duplexer is made compact and lightweight.
It is expected that mobile communication units, typical of which are an automobile phone and a portable phone, including this duplexer 1, will in the future continue to be made more compact and lightweight while being provided with higher functions. To achieve this target, it is inevitable to make the mounted duplexer 1 more compact and lightweight.
Since a conventional duplexer has a discrete filter and a switch mounted on a printed circuit board, however, it is difficult to make the duplexer more compact and lightweight. Especially in a filter, its performance and size are generally trade-offs. The higher the performance of the filter, the larger the dimensions, and therefore, the filter is prevented from being made compact and lightweight. Conversely, when the filter is made compact due to the size limitations of a mobile communication unit on which the duplexer is mounted, its filtering characteristics are insufficient and a compromise must be made on unit performance.